Lazily get names from UUIDs

Instead of doing the UUID->name resolution for all players in every
case, only do it when EntityId is accessed and the name hasn't been
retrieved this run already. This makes genPOI usable for people who
have many players on their servers but don't wish to use player POI
while still using other genPOI features.

To do this, a PlayerDict has been created, which contains a dirty
hack to see if the requested item is EntityId and whether it hasn't
been set already.
Merge pull request #1110 from CounterPillow/genpoi-triage

genPOI triage